The expression “operating device” is used in the present description and in the appended claims to indicate any device, implement, or tool that can be used in an industrial plant for carrying out an industrial operation.
A specific application that is described herein is that of a riveting device carried by a manipulator robot and designed to apply joining rivets on sheet-metal elements, for example in a motor-vehicle assembly line. A further example of application of the invention is that of an electric spot-welding gun carried by a manipulator robot or just simply a welding gun controlled manually by an operator. Yet a further example is constituted by a roller-hemming device carried by a manipulator robot.
In any application of the type referred to above there exists the problem of positioning and orienting the operating device properly with respect to the workpiece. Specifically, reference is here made to the case where the operating device has a main operative axis, having a predetermined position and orientation with respect to the operating device, and the piece has a surface that defines a preferential axis along which the operation must be performed, here referred to as “operation axis”, having a predetermined position and orientation with respect to the aforesaid surface of the piece.
In the case, for example, of a riveting device, it is in general necessary for the main operative axis of the device, corresponding to the direction of application of the rivet, to be orthogonal, within a predetermined margin of error, with respect to the surface portion of the piece (for example, an element of sheet metal) on which the operation itself is carried out. Likewise, in the case of a welding gun or in the case of a roller-hemming head, it is necessary for the tool to be correctly oriented with respect to the piece.
In the specific case of a motor-vehicle assembly line, the problem of proper orientation of an operating device, such as for example a riveting device or a welding gun, or a roller-hemming head, is rendered more complicated by that the sheet-metal constituting the structures to be processed may present a non-uniform quality, so that, even if the operating device is precisely positioned during preliminary set-up of the installation, defects may occur during normal production in the final produced structures.